This invention relates to composites of aliphatic alternating polyketones and other polymers such as polyolefins.
Combinations of polymers are commercially important because of their potential to combine valuable attributes of a number of different polymers. Blending polymers can give desirable combinations of attributes such as barrier and cost, chemical resistance and dimensional stability, and toughness and strength. Some examples of applications in which multilayer structures of two or more polymers are widely used include barrier packaging and pipe applications where the barrier properties of one material are combined with the mechanical properties of less expensive materials. Most polymer combinations have poor miscibility resulting in blends that are not a single phase. Nonmiscible polymers frequently do not have enough interaction to generate strong interfacial bonding. This weak interfacial bonding can lead to delamination and loss of properties. Compatibilization of the polymer/polymer interface refers to lowering interfacial tension or improving the physical or chemical interaction of the polymers in combination. It is of critical importance since it leads to the strong interfacial bonds necessary to achieve and maintain the desired properties of the combination. For example, it prevents or reduces the ingress of water and other liquids such as hydrocarbons.
Polymers of carbon monoxide and ethylenically unsaturated hydrocarbons commonly referred to as aliphatic alternating polyketones (hereafter, "polyketones") are now well known. High molecular weight alternating aliphatic polyketones are of considerable interest because they exhibit a good overall set of physical and chemical properties. They have excellent mechanical properties, chemical resistance, and barrier properties which makes them particularly attractive for use in combination with other polymers. This class of polymers is disclosed in numerous U.S. patents assigned to Shell Oil Company as exemplified by U.S. Pat. Nos. 4,880,903 and 5,369,170 which are incorporated herein by reference.
U.S. Pat. No. 5,369,170 to Weinkauf discloses a polymer composition which is a combination of a polyketone polymer, a polymer which is not miscible with the polyketone, and a compatibilizing polymer obtainable by reacting a diamine with a polymer having carboxyl groups. A maleic anhydride graft copolymer reacted with a diamine having two primary amino groups is such a compatibilizer. Graft or copolymerized acid copolymers (e.g., acrylic acid copolymers) also comprise such compatibilizers. Further refinements of this technology are discussed by Ash et. al. in Bonding Aliphatic Polyketones to Incompatible Polyolefin Polymers, Research Disclosures, January 1997, pp. 11,12 (Kenneth Mason Publications).
U.S. Pat. No. 5,637,410 to Bonner et. al. is directed to adhesive blends of polyolefins. The blends are carboxylic acid derivative graft polymers and a low density polyethylene reacted in the presence of a diamine. The preferred graft polymer is a maleic anhydride graft polyethylene. Multilayer structures made of these blends together with polyketones are also described.
The polymer compositions of the U.S. Pat. No. 5,369,170 patent can be produced in the form of a blend obtained by a melt blending process. In this type of process the compatibilizing polymer is thought to be present as a layer between the polyketone and the polymer to which it is bound. Multilayer structures can also be prepared by coextrusion to make such articles as multilayer pipes and multilayer sheets and films. The compatibilizing polymer can also be used as a coating layer for a polyketone object, in which case no second polymer need be present.
The preparation and use of the compositions of the U.S. Pat. Nos. 5,369,170 and 5,637,410 patents is not trouble free. For example, when the compatibilizers comprise maleated polymers, a stoichiometric excess of amine is typically required. Further, when the compatibilizers comprise carboxylic acid groups, as they may under the U.S. Pat. No. 5,369,170 patent, lengthy processing times in the melt can lead to increases in melt viscosity and a tendency to form gels. This can lead to poor melt stability, the formation of bubbles or lumps and an uneven distribution of layers in multilayer structures resulting in the so-called wave pattern in processed polymer. Further, the gels may deteriorate polymer performance by, for example, acting as stress concentrators thereby decreasing impact resistance. Without being bound to theory, it is believed that melt stability problems are caused by crosslinking.
Recently it has been found that improvements to multilayer structures using polyketones can be obtained by employing a compatibilizing polymer which is the reaction product of a particular type of amine and a polymer comprising carboxylic acid groups (i.e., hydroxycarbonyl groups). The amine comprises a primary amino group which is attached to an aliphatic carbon atom which carries at most one hydrogen atom. This affords some measure of steric hindrance to the amine. Compositions made from this combination show a reduced tendency to crosslink in the melt. While the interfacial attraction of the materials used in this combination is acceptable for many applications, further enhancements in adhesion are still desirable for many other applications.
Additional methods and compositions for combining polyketones with different polymers that lessen the propensity towards crosslinking and poor melt stability yet display improved interfacial attractions would enhance the utility of polyketones. This is particularly true in the case of multilayer structures and articles made from them.